Adolescence is the peak period of onset for serious and persistent psychiatric disorders. Treatment guidelines for the management of major psychiatric disorders in adolescence indicate pharmacotherapy is a critical element of effective treatment. Unfortunately, adolescence is a particularly vulnerable window for poor medication adherence, and little is known about the timecourse and specific factors associated with poor medication adherence in this population. Given that the consequences of poor medication adherence among youth with chronic mental illness are far-reaching, and include hospitalization, profound functional impairment and even suicide, there is a desperate need for interventions targeting medication adherence in this population. Motivational Interviewing (MI) is an evidence-based approach focused on enhancing motivation for change. This model holds great promise for improving medication adherence in adolescents with psychiatric disorders because it is developmentally sensitive, acceptable to patients and providers, and readily disseminable across clinical settings. Research demonstrates that brief motivational interventions (BMIs) utilizing a MI approach result in improved treatment adherence among youth with a variety of chronic medical conditions. Although widely applied for adolescent substance use behaviors, BMIs have yet to be examined for improving medication adherence in youth with severe psychiatric disorders. Adolescents with bipolar disorder (BP) are an ideal population with whom to develop a BMI for medication adherence because adolescents with BP are among the least adherent of any psychiatric population. Experience developing a BMI for this challenging population will directly inform intervention for youth with a range of chronic psychiatric disorders. The purpose of the proposed study is to conduct a 6-month naturalistic investigation (n=50) of the timing, trajectories, and specific demographic and clinical factors associated with poor medication adherence in this population. We will then develop and examine the feasibility of a BMI to improve medication adherence for adolescents initiating treatment at the Child and Adolescent Bipolar Services specialty clinic at Western Psychiatric Institute and Clinic. Sample selection will be informed by findings from the initial naturalistic study. Outcomes will be assessed monthly over 6 months. Participants will include 50 adolescents with BP. Given the range of options for assessing medication adherence in youth, we will also explore the feasibility and relative reliability of objective and subjective methods in this population. Data from this treatment development study will inform a full-scale controlled trial of this intervention. This approach is in direct accord with the NIMH Strategic Plan in which the development and testing of innovative interventions to reduce risk and positively alter trajectories of mental illness are informed by research findings regarding robust and malleable risk factors. Research in this area is of great public health importance, as it has the potential to lessen costs, disrupt the cycle of poor outcomes, and minimize the long-term debilitating effects of these serious disorders.